Millimeter wave spectrum of bromomethyl radical, CH2Br -: art. no. 134302

The rotational spectra of the two isotopic species of the bromomethyl radical, (CH2Br)-Br-79 and (CH2Br)-Br-81, have been observed in their ground electronic state B-2(1) in the 180-470 GHz frequency region, corresponding to a-type transitions from N=8-7 to N=21-20. The radical was produced by hydrogen abstraction of methylbromide (CH3Br) either by chlorine or by fluorine atoms in a free space cell. Hyperfine structure due to the bromine nucleus has been resolved in the observed spectra, and the rotational constants as well as the fine and hyperfine interaction constants were accurately determined for both isotopomers. The inertial defect was determined to be 0.028 96(20) and 0.028 95(20) amu angstrom(2), for (CH2Br)-Br-79 and (CH2Br)-Br-81, respectively, suggesting a planar structure. By fixing the angle HCH bond angle at 124.5 degrees, an effective molecular structure can be derived as r(0)(CBr)=1.848 A and r(0)(CH)=1.084 angstrom. A comparison of the molecular structure of various halogen-substituted methyl radicals with respect to the planarity of these radicals is discussed. (C) 2005 American Institute of Physics.